People have been asking, so here goes.

• Works with really large textbases without performance loss, yes.
• Windows cross-browser testing indicates compatibility with IE6, Firefox 1.0+, Opera 8. Netscape has yet to be tested. Konqueror has yet to be tested. Mozilla has yet to be tested.
• Mac cross-browser testing indicates compatibility with Firefox 1.0+, Safara 1.3.1, Camino 0.8.4.
• Mac IE5.2 does NOT work, but is on the to-do list.
• Downlevel browsers (Netscape 4, IE4) will probably choke and die. May flights of angels sing them to their rest. Okay, they won't die, stop crying, but they won't support AJAX Index Popups.

I've been working on a new incarnation of the Index Popup for Inmagic WebPublisher, which pages index lists and for fun, fetches pages the AJAX way. (Updates page content without refreshing the entire page.) This allowed me to create a find-as-you-type search box which acts like Google Suggest. Unbelievably satisfying. Also new is: i) ability to set field label different than field name; ii) selection builder so selections don't 'disappear'; iii) adjustable page size, and; iv) more. I'd like to do the same for validation lists, but they don't have a paging mechanism. And I won't go into the occult techniques I had to employ to get the index lists to page the way I wanted. Who knew backwards paging would be a herculean labour? Still, I'm very happy with it.